Optimal conditions for tissue culture growth of human umbilical vein endothelial cells under static and flow conditions will be established during the first 1 to 1-1/2 years of the proposed project. These cells will be grown, not only in standard culture flasks, but also in a rectangular chamber and in small ID tubes through which culture medium will be constantly circulated. The strength of attachment of endothelium to various supporting surfaces will be investigated under both static and flow conditions. Optimal conditions for long-term culture of endothelium will be studied. During the second and subsequent years of the proposed project, optimal conditions for recovery of adult arterial and venous endothelium from vascular segments will be established. These adult endothelial cells will be grown under both static and flow conditions in flasks, flow chambers, and tubes initially using information obtained from studies of optimal conditions for growth of fetal endothelial cells under these same conditions. Growth of adult arterial and venous cells will be optimized for both short-term and long-term studies, and effects of platelets and platelet products on growth of adult cells will be investigated. Endothelial cells grown in culture will be characterized by the production of factor VIII antigen and by the presence of cytoplasmic Weibel-Palade bodies. Finally, fetal and adult endothelial cells will be grown in straight, curved, and bifurcating tubes under conditions of constant culture medium flow in order to study shear effects on the endothelium. When this latter model system has been established, heparinized whole blood will be substituted for culture medium and endothelium subjected to varying shear stress will be examined subsequently by scanning and transmission electron microscopy.